Digital image processing is extensively applied to display systems. However, before digital signals prevailed, analog signal transmission dominated the field of data transmission between two different system interfaces. In analog signal transmission, only a data wire is needed for data transmission. In contrast, for digital signal transmission between two digital system, important components namely a digital-to-analog converter (DAC) and an analog-to-digital converter (ADC) are required. Taking digital pixel data generated by a graphic card of a personal computer, for example, the digital pixel data is converted by a DAC to corresponding analog pixel data that is then transmitted to an ADC in a digital display device. The ADC then converts the received analog pixel data to the corresponding digital pixel data that is to be displayed.
In a video signal processing system, e.g., a conventional analog television or a digital television, an ADC is generally implemented for converting an analog signal to digital signals, which makes performance and accuracy of the ADC crucial factors for display quality. A sampling frequency at which the ADC samples analog signals is determined by a sampling clock signal. In a conventional video signal mode applied to a personal computer monitor, an approach for detecting a sampling phase and a sampling frequency of analog signals is established under the premise that an image frame displayed on the personal computer monitor is still. More specifically, when a particular video signal mode is applied in video playback, detection of sampling phase needs to take variations between image frames into consideration since image variations substantially affect accuracy in the detection of sampling frequency and sampling phase. It is to be noted that, the sampling frequency of all video signal modes of analog video signals is fixed as being regulated by video specifications in advance, whereas the sampling phase needs to be determined. Therefore, there is a need for an apparatus for phase detection of dynamic analog video signals.